A generic filter device, a reversible flow filter device in particular, is disclosed in WO 98/42426. In the known reversible flow filter device, some of the filter elements used are made conical, especially in the form of tubular, wedge-wire screen filter elements. As a result of the conical execution, the distance between the individual conical wedge-wire screen filter elements or between them and cylindrical filter elements is increased, with the result that the outflow space in the filter housing is enlarged. Consequently, the offlow resistance in filter operation is reduced. During backflushing the conical filter element is obviously superior to a cylindrical one. First of all, this superiority is because of the relatively larger exit cross section of the conical filter elements compared to cylindrical ones for the same filter surface. Since the exit cross section for the conical filter elements compared to the entry cross section formed by the filter surface, that is to say, the free element area, is however relatively small, depending on the magnitude of the flow resistance of the slotted tube a bottleneck forms in which by large part of the system pressure falling off. Therefore, smaller pressure losses occur. This smaller pressure loss is more favorable in terms of energy during backflushing.
During backflushing, a large part of the volumetric throughput for conical and cylindrical filter elements is achieved basically on the bottom end of the filter. The volumetric flows then decrease very quickly. Since the conical element is essentially backflushed much farther, the velocity gradient is additionally smaller. With the inclusion of the velocity profiles relative to the filter surface as a result of the element conicity, an additional cleaning effect compared to cylindrical elements is then achieved. Due to the essentially constant velocity achieved in the cleaning of the conical filter elements, this flow takes place carefully prolonging the service life of these filter elements.
During backflushing, preferably all filter elements are regenerated in succession in chronological order. During backflushing of individual elements, filtration is continued over the remaining slotted tubes so that filtration operation in the known solution is never interrupted. The overpressure prevailing in the reversible flow filter device during the backflushing phase allows a small partial stream of filtrate to flow through the filter element to be cleaned in the reverse direction. The dirt is detached from the element and carried away. The amount of discharge accompanying backflushing cannot be exactly metered, and is based on empirical values. Generally, backflushing takes longer with large amounts in order to ensure reliable cleaning.
In the known solutions (WO 98/42426, DE 195 42 578 and DE 199 56 859), a hollow arm is pivoted to under one free entry cross section of the filter element to be cleaned and accordingly backflushed to remove the quantity of dirty backflushed fluid and from there the backflushed amount travels via the corresponding connecting pieces out of the filter housing for further treatment. In the known solutions, sealing problems arise with respect to connection of the flushing arm to the respective filter element to be backflushed. Otherwise, the pertinent discharge for the backflushed amount accordingly requires a large amount of installation space. Here, with respect to the number of fluid deflections for the backflushed amount, operating states which are unfavorable in terms of energy occur in the known solutions.